1. Field of the Invention
The present invention relates to an injector that controls opening/closing action of a needle by increasing/decreasing control pressure of a pressure control chamber through movement of a pressurizing piston driven by a piezoelectric actuator.
2. Description of Related Art
An injector using an electromagnetic valve as an actuator is commonly used. In order to realize a large flow rate and high response, an injector using a piezoelectric actuator with a large generative force and high response is proposed.
For example, an injector described in Patent document 1 (International Publication No. 2005/075811) has a piezoelectric actuator 100 that makes a displacement when voltage is applied thereto, a pressurizing piston 110 driven by the piezoelectric actuator 100, an outer sleeve 120 for slidably holding an outer periphery of the pressurizing piston 110, a pressure control chamber 130, internal pressure (hydraulic pressure) of which increases/decreases according to movement of the pressurizing piston 110, a needle 160 that is slidably held inside a valve body 140 and that opens/closes an injection hole 150 and the like as shown in FIG. 5.
The pressure control chamber 130 is fluid-tightly defined by the pressurizing piston 110, the outer sleeve 120, the needle 160 and the valve body 140. If the voltage is applied to the piezoelectric actuator 100, the piezoelectric actuator 100 pushes the pressurizing piston 110 downward in the drawing. Accordingly, the volume of the pressure control chamber 130 decreases and the internal pressure rises.
The internal pressure of the pressure control chamber 130 acts on a pressure receiving face 161 formed in the needle 160 to function as a valve opening force for biasing the needle 160 in a valve opening direction (upward direction in the drawing). If the valve opening force exceeds a valve closing force (reaction force of a spring 170 and the like) biasing the needle 160 in a valve closing direction, the needle 160 lifts and opens the injection hole 150. Thus, the high pressure fuel supplied to an inside of the valve body 140 is injected into a combustion chamber 180 of the engine from the injection hole 150.
However, the above-mentioned injector does not have a stopper mechanism for limiting a valve opening lift position of the needle 160 and the lift amount of the needle 160 is decided by the displacement amount of the piezoelectric actuator 100. Accordingly, there has been a problem that the injection quantity is not stabilized due to the displacement variation of the piezoelectric actuator 100.